1. Field of the Invention
The present invention relates generally to variable-gain mixers and amplifiers.
2. Description of the Related Art
Signal mixers are widely used for realizing frequency translation of an input signal by time domain multiplication with a second input signal. For example, mixers in wireless receivers and transmitters generally multiply an input signal with a local-oscillator (LO) signal tol thereby translate (i.e., convert) the input signal to a different mixer output signal. In particular, the time domain multiplication generates mixer output signals with frequencies that are the sum and difference of, the frequencies of the input and LO signals. A desired mixer output signal is typically selected with filters.
In many receivers and transmitters, a mixer is preceded by an amplifier whose gain is adjusted with an automatic gain control (AGC) feedback loop. These structures require substantial circuit space which is, severely limited in modern integrated-circuit wireless systems. In addition, integrated-circuit supply voltages have been constantly reduced (e.g., to 3.3 volts) because this permits finer interconnect structure which facilitates size reduction. The lowered supply voltage, however, limits the available headroom for circuit components which significantly complicates circuit design. These limitations have created a demand for simpler frequency-translation elements that can effectively operate with reduced supply voltages and provide greater accuracy.
The present invention is directed to digitally-controlled, variable-gain mixers that can be operated with reduced supply voltages and less current, that enhance accuracy and reduce spurious signals and that are less expensive in frequency translation applications because they eliminate components. The invention is also directed to digitally-controlled, variable-gain amplifiers and frequency converters.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.